The principal objective of this research program is to relate the genetic control of immunoglobulins to their chemical structure, biosynthesis and biological function. To achieve these objectives, we must develop monospecific antibodies to the genetic markers -- i.e., the allotypic specificities -- of rabbit Ig. By immunochemical analysis of family sera, genetic data will be obtained to evaluate issues of allelism and linkage. Rabbit colonies of defined genotype, homozygous or heterozygous for all known loci will be developed. The allotypic specificities are used as genetic markers for Ig molecules and cells synthesizing them. For the molecules, quantitative gene expression, allelic exclusion, and somatic recombination will be evaluated by quantitative radioprecipitation. The localization of allotypic specificities within the molecule will be evaluated by radioimmunoassay, peptide mapping, and amino acid composition of Ig fragments or subunits. For the cells, allelic exclusion and localization to cell populations will be assessed by fluorescent antibody. Cell surface Ig allotypes, cells secreting Ig allotypes, and cell sorting by allotype will be done with antibody-coated-erythrocytes as indicator cells for immunocytoadhesion and hemolytic plaques. Regulation of Ig biosynthesis will be investigated through study of homogeneous antibodies, allotype suppression, RNA-allotype-conversion, and cell-free-synthesis combined with antigen and mitogen stimulation. The mechanism of allotype-suppression will be investigated in an in vitro model and by sorting B and T cells. Allotype suppression in vivo by zygote transfer will be used to develop animals agammaglobulinemic for selected VH subgroups, Ig classes, or Ig types: a) to obtain large amounts of normally minor populations of Ig; b) to assess the biological requirements for Ig classes or types; c) to assess the limits of the gene pool. Attempts will be made to develop rabbit lymphoblastoid lines in culture and to develop an in vitro model for IgA synthesis. Finally, human Ig will be investigated for the presence, localization and genetic control crossreacting rabbit allotypic determinants.